Ultra-sonic flow meters are well known for measuring volumetric flow of liquids and gas. Ultra-sonic meters may be mounted within a pipe, mounted within a spool piece, or clamped onto the outer surface of the pipe. While ultra-sonic meters are suitable and in some case accurate flow meters, such as gas custody meters, ultra-sonic meters are not suitable for all fluid flows. For instance, ultra-sonic meters have difficulty measure volumetric flow rate when measuring aerated fluids. The gas bubbles scatter the ultra-sonic waves and therefore, provides an inaccurate or no output at all.
Similarly, an array-based flow meter that uses an array of sensors disposed along the pipe for measuring vortical disturbances and/or acoustic waves propagating through the flow, are suitable for some applications and not as suitable for other applications. The array-based flow meter and the ultra-sonic meter have common applications that they are both suitable for use, however, in other instances, the ultra-sonic meter functions better than the array-based meter in some applications and the array-based flow meter functions better than the ultra-sonic meter in other applications. The present invention combines the two technologies into a single flow meter to provide a flow meter capable of functions in a great number of applications than each flow meter can function alone.